The type of a one-frame planetary, diagonal rolling stand built in accordance with German Pat. No. 1,602,153 or U.S. Pat. No. 3,735,617 makes it possible, in the rolling of rod or light-section steel, to replace a complete roll line within the rod or light-section rolling mill train and to achieve in one rolling pass a considerable reduction in cross-section. This stand construction has made it possible to reduce considerably the plant expenditure for a rod or light-section steel train and also to reduce considerably the size of shed necessary for the housing of the rod and the light-section steel mill train. Commonly-used rod or light-section steel rolling mill trains usually use square-shaped billets as a raw material, these billets being gradually reduced to a circular cross-section by a large number of successive rolling passes. When using a planetary diagonal rolling mill in place of a complete preparation (break-down) line for the rod or light-section steel, the use of square billets as raw material leads to certain difficulties. This is because the lead end of the rod leaving the planetary diagonal rolling mill leaves as round stock, because of its peculiar mode of operation. The difficulties are mainly related to the fact that, during the initial rolling of a square bar, its corner areas are subjected to a considerably greater "working" during deformation than the other zones of the cross-section. This means that different material expansion takes place within the cross-section which influences the quality of the finished product disadvantageously.
From this it can be clearly understood that using round billets as raw material for rod or light-section steel rolling trains permit the roughing train to be replaced with a single-stand, planetary, diagonal rolling mill, because on that case the planetary diagonal rolling mill only has to cope with a cross-sectional reduction, but not with a cross-sectional deformation. Therefore, efficiency of a planetary diagonal rolling mill (that is, its operational safety and its degree of elongation) is considerably better in the rolling round raw stock than in the rolling of square cross-section billets.
In most steel mills, however, round bar stock is not always readily available in sufficient quantities, so that, as a practical matter, the replacement of a multi-stand roughing train in a rod or light-section steel rolling mill with a single-stand, planetary, diagonal rolling stand presents insurmountable difficulties. In order to fabricate round milling stock for use as a raw material, a complete new milling program must be created. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a rolling mill which eliminates many of the difficulties experienced in the past in a simple way and with small expenditure.
Another object of this invention is the provision of a process which uses octagonal cross-section billets and eliminates all difficulties and disadvantages, when these bars are subsequently treated in a planetary diagonal rolling stand.
It is another object of the instant invention to provide a process using octagonal cross-sections during rolling on a planetary diagonal rolling stand, whereby results are obtained equal to those that are achieved by the rolling of circular cross-section stock as the raw material.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.